1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly, to a frame buffer memory (simply referred to as "frame buffer" in the following) used in image processing.
2. Description of the Background Art
FIG. 6 is a block diagram showing a structure of a conventional general graphics system. As shown in FIG. 6, the graphics system includes: a system bus 100; a CPU (Central Processing Unit) 10 connected to system bus 100; a main memory 11 connected to system bus 100; a rendering controller 101 formed on a controller chip, and connected to system bus 100 and transferring the data stored in main memory 11; a frame buffer 102 connected to rendering controller 101 and storing the image data transferred; an RAM (Random Access Memory) digital-analog converter (RDAC) 103 connected to frame buffer 102 and responsive to a control signal received from rendering controller 101 for selectively outputting the image data provided from frame buffer 102; and a screen 104 connected to RDAC 103 and displays an image in accordance with the image data received.
Frame buffer 102 includes, for example, chips 102-1 to 102-4.
However, due to recent demand in enhanced performance for a graphics application and decrease in the price of memory, number of bits indicating information (information bit number) per pixel is increasing from 8 bits for indicating 256 colors to 16 bits for "index color", and further to 24 bits for "true color".
Furthermore, a recent graphics application has a double-buffer structure for enabling CRT (Cathode-Ray Tube) refresh operation for transmitting data from a frame buffer to an RDAC and write operation (rendering) for writing data to a frame buffer simultaneously, and switches between overlay image plane and RGB (Red-Green-Blue. Accordingly, information bit number per pixel is even increasing.
Therefore, the problem associated with a conventional graphics system shown in FIG. 6 is that the required number of output terminals increases as information bit number per pixel increases in its frame buffer 102, thereby resulting in the difficulty in manufacturing a package, board wiring or the like, as well as in the increase in manufacturing cost.